In team water sports is, such as water polo, it is conventional for members of each team to wear distinctive outer head wear so as to distinguish members of one team from those of the opposing team. Normally such head wear for one team is usually white or a light color and for the opposing team, a dark color. The outer head wear is a single size and it fits relatively loosely on the players head. Accordingly, it is conventional, particularly for female players, to wear a hair retaining cap under the outer cap.
In the course of engaging in the water sport, the outer cap will often move on the players head exposing a portion of the under cap. If the under cap is not similar in color to the outer cap it may appear that the player is a member of the opposing team whose outer cap resembles the players hair retaining under cap and which may result in possible confusion. For this reason water sports such as water polo have rules that require that the under cap resemble the outer cap in appearance. That is, if the outer cap is white or light-colored the under cap must also be white or light colored. Likewise, if the outer cap is dark the under cap must also be of the dark color. It is conventional for players to purchase and carry with them two under caps, a light and a dark cap, to accommodate the particular color of the outer cap.